Multiple status e-fuse based non-volatile voltage control oscillator configured for process variation compensation, an associated method and an associated design structure

ABSTRACT

Disclosed are embodiments of a voltage controlled oscillator (VCO) capable of non-volatile self-correction to compensate for process variations and to ensure that the center frequency of the oscillator is maintained within a predetermined frequency range. This VCO incorporates a pair of varactors connected in parallel to an inductor-capacitor (LC) tank circuit for outputting a periodic signal having a frequency that is proportional to an input voltage. A control loop uses a programmable variable resistance e-fuse to set a compensation voltage to be applied to the pair of varactors. By adjusting the compensation voltage, the capacitance of the pair of varactors can be adjusted in order to selectively increase or decrease the frequency of the periodic signal in response to a set input voltage and, thereby to bring the frequency of that periodic signal into the predetermined frequency range. Also disclosed are embodiments of an associated design structure for such a VCO and an associated method for operating such a VCO.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/057,494 filed Mar. 28, 2008 and assigned to the present Assignee.

BACKGROUND OF THE INVENTION

The embodiments of the invention generally relate to the frequency rangeof voltage control oscillators (VCOs) and, more particularly, to a VCOconfigured with a control loop that incorporates variable resistancee-fuse(s) to selectively adjust the periodic output signal frequency tocompensate the process variation. The embodiments also relate to anassociated design structure for such a VCO and to an associated methodfor operating such a VCO.

DESCRIPTION OF THE RELATED ART

Process variations impact performance in all technologies. In voltagecontrolled oscillators (VCOs) such process variations can have asignificant impact on operation frequency. Specifically, with continueddevice scaling, process variations can impact the operational frequencyrange of a VCO such that it is no longer within specification.Therefore, it would be advantageous to provide a VCO capable ofnon-volatile self-correction to compensate for process variations and,thereby to ensure that the center frequency is maintained within thepredetermined frequency range.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing disclosed herein are embodiments of a voltagecontrolled oscillator (VCO) capable of non-volatile self-correction tocompensate for process variations and, thereby to ensure that the centerfrequency of the VCO is maintained within a predetermined frequencyrange. Embodiments of this VCO incorporate a pair of varactors connectedin parallel to an inductor-capacitor (LC) tank circuit for outputting aperiodic signal having a frequency that varies as a function of an inputvoltage (e.g., increases with an increasing input voltage, decreaseswith a decreasing input voltage). The embodiments further incorporate acontrol loop. This control loop uses programmable variable resistancee-fuse(s) to set a compensation voltage to be applied to the pair ofvaractors. By adjusting the compensation voltage, the capacitance of thepair of varactors can be adjusted in order to selectively increase ordecrease the frequency of the periodic signal in response to an inputvoltage and, thereby bring the frequency of that periodic signal intothe predetermined frequency range.

More particularly, disclosed herein are embodiments of a voltagecontrolled oscillator (VCO). The VCO embodiments can comprise aninductor-capacitor (LC) tank adapted to receive a first voltage (i.e., asupplied input voltage in an operating mode or a predetermined tuninginput voltage in a sensing mode) for controlling capacitance in the LCtank and at least one varactor connected in parallel with the LC tankand adapted to receive a second voltage (i.e., a compensation voltage)for controlling capacitance in the varactor(s).

The VCO embodiments can further comprise a VCO output node that isconnected to the LC tank and the varactor(s) and that is adapted tooutput a periodic signal that is generated by the parallel connected LCtank and varactor(s). Thus, the frequency of the periodic signal at theVCO output node will be a function (e.g., an increase function) of thefirst voltage (i.e., the supplied or tuning input voltage) and, ifnecessary, can also be a function of a second voltage (i.e., acompensation voltage). An amplifier can be connected between theparallel connected LC tank and varactor(s) and the VCO output node andcan be adapted to adjust (i.e., magnify) this periodic signal.

Additionally, the VCO embodiments can comprise a control loop betweenthe VCO output node and the varactor(s). This control loop can beadapted to determine if the frequency of the periodic signal at the VCOoutput node in response to a set first voltage (i.e., a predeterminedtuning input voltage) is outside a predetermined frequency range and, ifnecessary, can be adapted to bring that frequency back into thepredetermined frequency range by determining the required second voltage(i.e., the required compensation voltage) and applying that secondvoltage to the varactor(s).

Specifically, the control loop can comprise a period detector connectedto the VCO output node. This period detector can be adapted to determinethe period of the periodic signal at the VCO output node and to convertthat period into an output voltage. The control loop can furthercomprise a plurality of voltage comparators adapted to determine if theoutput voltage of the period detector is within a predetermined voltagerange. For example, a first comparator can compare the output voltage ofthe period detector to the upper limit of the predetermined voltagerange to determine if the frequency of the periodic signal at the VCOoutput node needs to be increased. Additionally, a second comparator cancompare the output voltage of the period detector to the lower limit ofthe predetermined voltage range to determine if the frequency of theperiodic signal at the VCO output node needs to be decreased.

The control loop can also comprise a variable resistance e-fuse adaptedto apply the second voltage to the varactor(s) and a controller adaptedto program the resistance in the variable resistance e-fuse, when thefrequency is outside a predetermined frequency range, so as toselectively adjust the second voltage, so as to adjust the capacitanceof the varactor(s), and further so as to bring the frequency of theperiodic signal to within the predetermined frequency range. That is,the variable (i.e., programmable) resistance e-fuse can be electricallyconnected to the controller and to the varactor(s). The controller canbe in communication with the plurality of comparators and can be adaptedto program the resistance in the variable resistance e-fuse, when thefrequency of the periodic signal at the VCO output node is outside thepredetermined frequency range (i.e., when the output voltage from theperiod detector is outside the predetermined voltage range).

Programming of the e-fuse resistance is performed so as to selectivelyadjust the compensation voltage that will be applied to the varactor(s)during subsequent VCO operation, so as to selectively adjust thecapacitance of the varactor(s), and further so as to bring the frequencyof the periodic signal at the VCO output node to within thepredetermined frequency range. For example, the controller can beadapted to selectively increase the resistance in the variableresistance e-fuse so as to selectively increase the compensation voltageat the varactor(s) in order to decrease the capacitance of thevaractor(s) and, thereby increase the frequency of the periodic signalat the VCO output node, when the output voltage from the period detectoris higher than the predetermined voltage range. The controller canfurther be adapted to selectively decrease the resistance of thevariable resistance e-fuse so as to selectively decrease thecompensation voltage at the varactor(s) in order to increase thecapacitance of the varactor(s) and, thereby decrease the frequency ofthe periodic signal at the VCO output node, when the output voltage islower than the predetermined voltage range.

An exemplary variable resistance e-fuse that can be incorporated intothe present invention can comprise a non-volatile, re-programmable,bi-directional e-fuse. Specifically, this e-fuse can comprise aconductor, a plurality of series connected resistors and a plurality ofcopper contacts on the conductor connected to the plurality of theseries connected resistors. The resistors can all be equal in size.

Additionally, first and second sensing nodes can be located on oppositeends of the series connected resistors. The first sensing node can beelectrically connected to the varactor(s) and to a first current sourcevia a switch. The second sensing node can be electrically connected viaa switch to ground. During a sensing mode, the controller can be adaptedto turn on these switches allowing the sensing current to flow from thefirst current source through the conductor of the variable resistancee-fuse between the first sensing node and the second sensing node inorder to generate the second voltage (i.e., the compensation voltage) atthe varactor(s). As mentioned above, the frequency of the periodicsignal at the VCO output node is a function of the first voltage (i.e.,the predetermined tuning voltage in the sensing mode) applied to theLC-tank and also a function of the second voltage (i.e., thecompensation voltage) applied on the varactor(s).

First and second programming nodes can also be located on opposite endsof the conductor. The first and second programming nodes can each beconnected by complementary switches to a second current source which isdifferent from the first current source and to ground. During aprogramming mode, the controller can be adapted to use the switches tocontrol a second current flow from this second current source to programthe resistance in the variable resistance e-fuse. Specifically, thecontroller can be adapted to use the switches to control the flow of thesecond current through the conductor between the first programming nodeand the second programming node such that the second current flows inone direction from the first programming node (i.e., an anodeprogramming node) to the second programming node (i.e., a cathodeprogramming node), causing the contacts near the second programming nodeto become opens in sequence to increase the resistance; or such that thesecond current flows in the opposite direction from the secondprogramming node (i.e., the anode programming) to the first programmingnode (i.e., the cathode programming node), causing the opened contactsnear the second programming node to revert back to shorts in sequence todecrease the resistance. Note that the open contact sequence directionis in the direction of the electron flow from the cathode node to theanode node, which is opposite to the direction of the current flow fromthe anode node to the cathode node. Thus, the programming isbi-directional. Furthermore, due to the variable resistance e-fusestructure, the resulting resistance following programming isnon-volatile (i.e., it is maintained even after the circuit is powereddown), but reprogrammable on demand.

The embodiments of the voltage controlled oscillator are described aboveas incorporating only a single variable resistance e-fuse.Alternatively, the voltage controlled oscillator can comprise aplurality of such variable resistance e-fuses. Specifically, multiplevariable resistance e-fuses can be connected in series. In this case,all of the resistors in any given variable resistance e-fuse will beequal in size. However, the resistors on adjacent variable resistancee-fuses will be progressively smaller in size. Such a structure allowsfor fine tuning of the frequency the periodic signal at the output nodebecause each subsequent e-fuse can be programmed in order to makesmaller incremental changes in overall resistance and, thereby to makesmaller incremental changes to the compensation voltage applied to thevaractor(s).

Also disclosed herein are embodiments of an associated method foroperating a voltage controlled oscillator (VCO). The method embodimentscomprise providing a VCO, such as the VCO described in detail above.That is, the provided VCO can comprise an inductor-capacitor (LC) tankcircuit adapted to receive a first voltage (i.e., a supplied or tuninginput voltage) and at least one varactor connected in parallel with theinductor-capacitor (LC) tank circuit and adapted to receive a secondvoltage (i.e., a compensation voltage) such that the VCO output can be afunction of the first voltage and, if necessary, a second voltage.

Next, the VCO is powered up for the first time and a control loop isestablished within the VCO. In this control loop, the VCO is operated insuccessive sensing and programming modes. The sensing mode comprisesdetermining whether the frequency of the periodic signal at the VCOoutput node in response to a set first voltage (i.e., a predeterminedtuning input voltage) is within a predetermined frequency range. If,during the sensing mode, a determination is made that the frequency isoutside the predetermined range, then the VCO enters the programmingmode. The programming mode comprises, programming (i.e., selectivelyincreasing or decreasing) the resistance in a variable resistancee-fuse, as necessary, to set the second voltage (i.e., the compensationvoltage) to be applied to the varactor(s) and, thereby to bring thefrequency of the periodic signal at the VCO output node into thepredetermined frequency range.

During the sensing mode, the process of determining whether or not thefrequency of the periodic signal at the VCO output node in response to aset first voltage (i.e., a predetermined tuning input voltage) is withinthe predetermined frequency range can be accomplished by determining aperiod of this periodic signal. The detected period can be convertedinto an output voltage. Through prior simulation and testing, it can bedetermined that an output voltage that is above an upper limit of apredetermined voltage range indicates that the period is too long. Thisin turn will indicate that the frequency of the periodic signal at theoutput node is too low. Similarly, an output voltage that is below alower limit of the predetermined voltage range indicates that the periodis too short. This in turn indicates that the frequency of the periodicsignal at the output node is too high. Thus, once the output voltage isdetermined, it can be determined if the output voltage is within apredetermined voltage range and the frequency of the periodic signal atthe VCO output node can be adjusted accordingly, during the programmingmode.

For example, the output voltage can be compared to the upper limit ofthe predetermined voltage range to determine if the frequency of theperiodic signal needs to be increased. Then, the resistance in thevariable resistance e-fuse can be selectively increased so as toselectively increase the compensation voltage applied to the varactor(s)in order to selectively decrease the capacitance of the varactor(s) and,thereby to increase the frequency of the periodic signal at the VCOoutput node, when the output voltage is higher than the predeterminedvoltage range. Additionally, the output voltage can be compared to thelower limit of the predetermined voltage range to determine if thefrequency of the periodic signal needs to be decreased. Then, theresistance in the variable resistance e-fuse can be selectivelydecreased so as to selectively decrease the compensation voltage at thevaractor(s) in order to selectively increase the capacitance of thevaractor(s), and thereby to decrease the frequency of the periodicsignal at the VCO output node, when the output voltage is lower than thepredetermined voltage range.

In the sensing mode, a first current from a first current source isforced to flow through the variable resistance e-fuse to the ground inorder to generate the compensation voltage at the varactor(s). This samecurrent can be forced to flow through the variable resistance e-fuse inorder to generate the set compensation voltage, during subsequentstandard operation (e.g., when a periodic signal is generated at the VCOoutput node in response to a supplied input voltage from an outsidedevice, such as a filter in a phase locked loop (PLL) circuit).Contrarily, in the programming mode, a second current from a secondcurrent source different from the first current source is forced to flowthrough the variable resistance e-fuse in one direction or another toprogram the resistance therein without applying a second voltage (i.e.,a compensation voltage) to the varactor(s).

The embodiments of the method are described above as including aprogramming step for only one variable resistance e-fuse. Alternatively,the voltage controlled oscillator can comprise a plurality of suchvariable resistance e-fuses. Specifically, multiple variable resistancee-fuses can be connected in series. In this case, all of the resistorsin any given variable resistance e-fuse will be equal in size. However,the resistors on adjacent variable resistance e-fuses will beprogressively smaller in size. Such a structure allows for fine tuningof the frequency the periodic signal at the output node because eachsubsequent e-fuse can be programmed in order to make smaller incrementalchanges in overall resistance and, thereby to make smaller incrementalchanges to the compensation voltage applied to the varactor(s).

Also disclosed are embodiments of a design structure for the abovedescribed voltage controlled oscillator. This design structure can beembodied in a machine readable medium, can reside on storage medium as adata format used for the exchange of layout data of integrated circuitsand can comprise, for example, a netlist.

These and other aspects of the embodiments of the invention will bebetter appreciated and understood when considered in conjunction withthe following description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingembodiments of the invention and numerous specific details thereof, aregiven by way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments withoutdeparting from the spirit thereof, and the embodiments include all suchchanges and modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention will be better understood from thefollowing detailed description with reference to the drawings, in which:

FIG. 1 is a schematic diagram illustrating an embodiment of a voltagecontrolled oscillator (VCO);

FIG. 2 a is a diagram illustrating an exemplary programming processwherein resistance is increased in a variable resistance e-fuse;

FIG. 2 b is a diagram illustrating an exemplary programming processwherein resistance is decreased in a variable resistance e-fuse;

FIG. 3 is a schematic diagram illustrating an alternative configurationfor the VCO of FIG. 1 incorporating multiple series connected e-fuses;

FIG. 4 is a diagram illustrating an exemplary phase locked loop (PLL)circuit that can incorporate the VCO of FIG. 1;

FIG. 5 is a flow diagram illustrating an embodiment of a method foroperating a VCO; and

FIG. 6 is a flow diagram of a design process used in semiconductordesign, manufacture, and/or test.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the invention and the various features andadvantageous details thereof are explained more fully with reference tothe non-limiting embodiments that are illustrated in the accompanyingdrawings and detailed in the following description. It should be notedthat the features illustrated in the drawings are not necessarily drawnto scale. Descriptions of well-known components and processingtechniques are omitted so as to not unnecessarily obscure theembodiments of the invention. The examples used herein are intendedmerely to facilitate an understanding of ways in which the embodimentsof the invention may be practiced and to further enable those of skillin the art to practice the embodiments of the invention. Accordingly,the examples should not be construed as limiting the scope of theembodiments of the invention.

As mentioned above, process variations impact performance in alltechnologies. In voltage controlled oscillators (VCOs) such processvariations can have a significant impact on operation frequency.Specifically, with continued device scaling, process variations canimpact the operational frequency range of a VCO such that it is nolonger within specification. One conventional solution is to increasethe VCO frequency coverage by using a small inductance in theinductor-capacitor (LC) tank within the VCO. One disadvantage of such asolution is the fact that small inductance in the LC tank reduces the Qvalue of the LC tank such that phase noise is increased. Anotherdisadvantage is the fact that the VCO will operate in a different partof the VCO frequency coverage and the VCO gain will be different.Consequently, it is difficult to achieve the specifications required fora given circuit (e.g., a phase locked loop) that is to incorporate theVCO. Since once a product is manufactured the impact of such processvariations on operation frequency is fixed, it would be advantageous toprovide a voltage controlled oscillator capable of non-volatileself-correction to compensate for process variations and to ensure thatthe center frequency is maintained within the predetermined frequencyrange.

In view of the foregoing disclosed herein are embodiments of a voltagecontrolled oscillator (VCO) capable of non-volatile self-correction tocompensate for process variations and, thereby to ensure that the centerfrequency of the VCO is maintained within a predetermined frequencyrange. Embodiments of this VCO incorporate a pair of varactors connectedin parallel to an inductor-capacitor (LC) tank circuit for outputting aperiodic signal having a frequency that varies as a function of an inputvoltage (e.g., increases with an increasing input voltage, decreaseswith a decreasing input voltage). The embodiments further incorporate acontrol loop. This control loop uses programmable variable resistancee-fuse(s) to set a compensation voltage to be applied to the pair ofvaractors. By adjusting the compensation voltage, the capacitance of thepair of varactors can be adjusted in order to selectively increase ordecrease the frequency of the periodic signal in response to an inputvoltage and, thereby bring the frequency of that periodic signal intothe predetermined frequency range.

Referring to FIG. 1, disclosed herein are embodiments of a voltagecontrolled oscillator (VCO) 100. The VCO embodiments 100 can comprise aninductor-capacitor (LC) tank 110 adapted to receive a first voltage 121(i.e., a supplied input voltage in an operating mode or a predeterminedtuning input voltage in a sensing mode) for controlling capacitance inthe LC tank 110 and at least one varactor 113 connected in parallel withthe LC tank 110 and adapted to receive a second voltage 122 (i.e., acompensation voltage) for controlling capacitance in the varactor(s)113. The VCO embodiments 100 can further comprise a VCO output node 102that is connected to the LC tank 110 and the varactor(s) 113 and that isadapted to output a periodic signal that is generated by the parallelconnected LC tank 110 and varactor(s) 113. Thus, the frequency 123 ofthe periodic signal at the VCO output node 102 will be a function (e.g.,an increase function) of the first voltage 121 (i.e., the supplied ortuning input voltage) and, if necessary, can also be a function of thesecond voltage 122 (i.e., the compensation voltage).

Additionally, the VCO embodiments 100 can comprise a control loopbetween the VCO output node 102 and the varactor(s) 113 connected inparallel with the LC tank 110. This control loop can be adapted todetermine if the frequency 123 of the periodic signal at the VCO outputnode 102 in response to a set first voltage 121 (i.e., a predeterminedtuning input voltage) is outside a predetermined frequency range and, ifnecessary, can be adapted to bring that frequency back into thepredetermined frequency range by determining the required second voltage122 (i.e., the required compensation voltage) and applying that secondvoltage 122 to the varactor(s) 113 during subsequent sensing and/oroperational modes.

More specifically, the VCO 100 embodiments comprise an input node 101,an output node 102, and an inductor-capacitor (LC) tank circuit 110. TheLC tank circuit 110 can, for example, comprise an inductor 111 connectedin parallel to at least one variable capacitor or varactor 112. Forexample, the inductor 111 can be connected in parallel to a first pairof series connected varactors. A first voltage 121 received at the inputnode 101 can control the capacitance of varactor(s) 112 in the LC tank110.

As discussed in greater detail below, the source of the input voltage121 will change depending upon whether the VCO 100 is in sensing andprogramming modes or in a standard operational mode. That is, in thesensing and programming modes, the first voltage 121 at the input node101 can be a predetermined tuning input voltage. Contrarily, in astandard operational mode, the first voltage 121 at the input node 101can be a supplied input voltage from an external device (e.g., a filterof a phase locked loop (PLL) circuit).

The VCO 100 embodiments can further comprise at least one varactor 113that is connected in parallel with the LC tank circuit 110. For example,a second pair of series connected varactors 113 can be connected inparallel to the LC tank circuit 110. A second voltage (i.e., acompensation voltage) applied to the varactor(s) 113 (e.g., at node 103)can control the capacitance of the varactor(s) 113.

The parallel connected LC tank circuit 110 and varactor(s) 113 areconfigured such that the frequency 123 of the periodic signal at theoutput node 102 is a function of both the first voltage 121 and thesecond voltage 122. For example, increasing or decreasing either of thevoltages 121 or 122 will result in a corresponding increase or decrease,respectively, in the frequency 123 of the periodic signal at the outputnode 102. An amplifier 130 connected between the VCO output node 102 andthe LC tank with the varactor(s) 113 can magnify this periodic signal.

The VCO 100 embodiments can also comprise a control loop for determiningif the frequency 123 of the periodic signal at the output node 102 inresponse to a set input voltage 121 (i.e., in response to apredetermined tuning input voltage) is outside a predetermined frequencyrange and, if necessary, for bringing that frequency 123 back into thepredetermined frequency range by determining the required second voltage122 (i.e., the required compensation voltage) and applying that secondvoltage 122 to the varactor(s) 113. Specifically, the control loop cancomprise a period detector 140 connected to the VCO output node 102.This period detector 140 can be adapted to determine the period of theperiodic signal at the output node 102 and to convert that period intoan output voltage 124. Through simulation and testing, it can bedetermined that an output voltage 124 that is above an upper limit of apredetermined voltage range indicates that the period is too long. Thisin turn will indicate that the frequency of the periodic signal at theoutput node is too low. Similarly, an output voltage 124 that is below alower limit of the predetermined voltage range indicates that the periodis too short. This in turn indicates that the frequency 123 of theperiodic signal at the output node 102 is too high.

Thus, the control loop can further comprise a plurality of voltagecomparators 151-152 adapted to determine if the output voltage 124 ofthe period detector 140 is within a predetermined voltage range. Forexample, a first comparator 151 can compare the output voltage 124 ofthe period detector 140 to the upper limit (i.e., Vth_up 125) of thepredetermined voltage range to determine if the frequency 123 of theperiodic signal at the VCO output node 102 needs to be increased.Additionally, a second comparator 152 can compare the output voltage 124of the period detector 140 to the lower limit (i.e., Vth_low 126) of thepredetermined voltage range to determine if the frequency 123 of theperiodic signal at the VCO output node 102 needs to be decreased.

The control loop can also comprise a variable (i.e., programmable)resistance e-fuse 170 electrically connected to the varactor(s) 113(e.g., at node 103) for applying a compensation voltage 122 (i.e., asecond voltage) to those varactor(s) 113, as necessary, in order toadjust the frequency 123 of the periodic signal at the VCO output node102. The variable resistance e-fuse 170 can also be electricallyconnected to a controller 160 for programming the variable resistancee-fuse 170 to ensure that the proper compensation voltage 122 isapplied.

More specifically, increasing or decreasing the frequency 123 of theperiodic signal at the VCO output node 102 can be accomplished bydecreasing or increasing, respectively, the capacitance of thevaractor(s) 113. Increasing or decreasing the capacitance of thevaractor(s) 113 can in turn be accomplished by decreasing or increasing,respectively, the compensation voltage 122 applied to the varactors(s)113. Finally, increasing or decreasing the compensation voltage 122applied to the varactor(s) 113 can in turn be accomplished by increasingor decreasing, respectively, the resistance of the variable resistancee-fuse 170. Once the compensation voltage 122 is set, it will be appliedto the varactor(s) 113 during subsequent sensing operations and alsoduring normal VCO 100 operations to compensate for process variations.

To accomplish this, the controller 160 is in communication with theplurality of comparators 151-152. The controller 160 is adapted toprogram the resistance in the variable resistance e-fuse 170, when thefrequency 123 of the periodic signal at the VCO output node 102 inresponse to a set input voltage 121 is outside the predeterminedfrequency range (i.e., when the output voltage 124 from the perioddetector 140 is outside the predetermined voltage range or morespecifically, either above the upper limit 125 or below the lower limit126). Programming the resistance is performed so as to selectivelyadjust the compensation voltage 122 at the varactor(s) 113, so as toselectively adjust the capacitance of the varactor(s) 113, and furtherso as bring the frequency 122 of the periodic signal at the VCO outputnode 102 to within the predetermined frequency range.

For example, the controller 160 can be adapted to selectively increasethe resistance in the variable resistance e-fuse 170 so as toselectively increase the compensation voltage 122 at the varactor(s) 113in order to decrease the capacitance of the varactor(s) 113 and, therebyincrease the frequency 122 of the periodic signal at the VCO output node102, when the output voltage 124 from the period detector 140 is higherthan the upper limit of the predetermined voltage range. The controller160 can further be adapted to selectively decrease the resistance of thevariable resistance e-fuse 170 so as to selectively decrease thecompensation voltage 122 at the varactor(s) 113 in order to increase thecapacitance of the varactor(s) 113 and, thereby decrease the frequency122 of the periodic signal at the VCO output node 102, when the outputvoltage 124 is lower than the low limit of the predetermined voltagerange.

An exemplary variable resistance e-fuse 170 that can be incorporatedinto the present invention can comprise a non-volatile, re-programmable,bi-directional e-fuse. Specifically, this e-fuse 170 can comprise aconductor 175, a plurality of series connected resistors 177 (i.e., aresistor bank) and a plurality of metal contacts 176 (e.g., copper (Cu)or tungsten (W) contacts) on the conductor 175 and connected to theplurality of the series connected resistors 177, as illustrated. Theresistors 177 can all be equal in size.

First and second sensing nodes 171, 172 can be located on opposite endsof the resistor bank (i.e., on opposite ends of the series connectedresistors 177). The first sensing node 171 can be electrically connectedto the varactor(s) 113 and to a first current source 181 via a switch191 (e.g., a p-type field effect transistor (PFET)). The second sensingnode 172 can be electrically connected via a switch 192 (e.g., an n-typefield effect transistor (NFET)) to ground 183. During a sensing mode(and also during an operational mode), the controller 160 can be adaptedto turn on these switches 191-192 allowing the first current to flowfrom the sensing current source 181 through the metal conductor wire 175(e.g., copper wire) of the variable resistance e-fuse 170 between thefirst sensing node 171 and the second sensing node 172 to ground 183 inorder to generate the compensation voltage 122 at the varactor(s) 113.During the sensing mode, a set input voltage (i.e., a predeterminedtuning input voltage) is applied to the VCO input node 101. During theoperational mode, the frequency of the periodic signal at the VCO outputnode is an increase function of a first voltage 121 that comprises asupplied input voltage from another device (e.g., from the filter of aphase locked loop circuit). It should be noted that during the sensingand standard operational modes, switches 193-196, discussed in greaterdetail below with regard to programming, are turned off so that thesecond current from the second current source 182 does not pass throughthe e-fuse 170.

First and second programming nodes 173, 174 can also be located onopposite ends of the conductor 175. The first and second programmingnodes 173, 174 can each be connected by complementary switches 193-194,195-196 (e.g., NFETs and PFETs) to a second current source 182 which isdifferent from the first current source 181 and to ground 183. Duringthe programming mode, the controller 160 can be adapted to use theswitches 193-196 to control second current flow from this second currentsource 182 to program resistance in the variable resistance e-fuse 170.

Programming in the e-fuse 170 is bi-directional, taking advantage ofelectro-migration in the metal (such as copper) conductor wire 175 inresponse to applied currents (e.g., as described in U.S. patentapplication Ser. No. 11/839,716, filed Aug. 16, 2007, the entiredisclosure of which is incorporated herein by reference). Specifically,the controller 160 can be adapted to use the switches 193,196 to controlthe flow of the second current through the conductor 175 between thefirst programming node 173 (i.e., the anode programming node) and thesecond programming node 174 (i.e., the cathode programming node) suchthat the second current flows in one direction causing the contacts 176near the cathode end of the conductor wire 175 to become opens 201 insequence to increase the resistance (e.g., as illustrated in FIG. 2 a)or such that the second current flows in the opposite direction causingthe previously opened contacts 176 to revert back to shorts 202 insequence to decrease the resistance (e.g., as illustrated in FIG. 2 b).It should be noted that during this programming mode, switches 191-192,discussed above, are turned off so that current from current source 181does not generate voltage at the varactor(s) 113 and, thereby impact thecapacitance in the varactor(s) 113.

The sensing and programming processes, described above, are repeated bythe controller 170 until the frequency 123 of the periodic signal at theoutput node 102 is found to be within the predetermined frequency range.Once programming is complete, the resulting resistance in the e-fuse 170is non-volatile (i.e., it is maintained even after the circuit ispowered down). Thus, the VCO 100 can be repeatedly powered up withouthaving to reprogram the resistance in the e-fuse 170 to achieve thedesired voltage compensation. However, the resistance is not fixedpermanently. Thus, if it is necessary to alter the center frequency ofthe VCO 100 for any reason, the e-fuse 170 can be reprogrammed ondemand.

The embodiments of the VCO 100 are described above and illustrated inFIG. 1 as incorporating only a single variable resistance e-fuse 170.Alternatively, as illustrated in FIG. 3, the VCO 100 can comprise aplurality of such variable resistance e-fuses 170 a-c. Specifically,multiple variable resistance e-fuses 170 a-c can be connected in series.In this case, all of the resistors in any given variable resistancee-fuse 170 a-c will be equal in size. However, the resistors (e.g., 177a, 177 b, 177 c) on adjacent variable resistance e-fuses 170 a-c will beprogressively smaller in size (e.g., R for 177 a, R/10 for 177 b, R/100for 177 c, etc.). Such a structure allows for fine tuning of thefrequency 123 of the periodic signal at the output node 102 because eachsubsequent e-fuse (e.g., 170 a then 170 b then 170 c) can be programmedin sequence in order to make smaller incremental changes in overallresistance and, thereby to make smaller incremental changes to thecompensation voltage 122 applied to the varactor(s) 113. Thus,compensation resolution can be improved.

FIG. 4 represents an exemplary phase locked loop (PLL) circuit 400 thatcan incorporate the VCO 100 of the present invention. Specifically, thePLL circuit 400 can comprise a phase/frequency detector (PFD) 401, acharge pump 402, a low-pass filter 403, the VCO 100, and a divide-by-Ncounter 405. The PLL 400 is a negative feed back circuit. That is,during normal PLL operation, the phase/frequency detector 401 is adaptedto detect the phase/frequency difference between a reference frequencyf_(in) and the feedback frequency f_(fbk) (e.g., the output frequencyf_(out) 123 of the VCO 100 after passing through a divide-by-N counter405) and to signal to the charge pump 402 to increase or decrease thefrequency of the VCO 100, as necessary. For example, if f_(in) isoperating at a slightly faster frequency than f_(fbk), the PFD 401 canoutput an UP signal to the charge pump 402. Contrarily, if f_(in) isoperating at a slightly slower frequency than f_(fbk), the PFD 401 canoutput a DOWN signal to the charge pump 402. The loop filter 403 makessure that the voltage 412 (Vfilter) applied to the VCO 100 changesgradually and prevents spiking attributes or system instable.

During normal PLL operations, the signal 407 will be set (e.g., by thecontroller 170) at logic low so that the switch 409 (e.g., a PFET) isturned on and the switch 410 (e.g., also a PFET) is turned off. Thus,during normal PLL operations, the first voltage 121 to the VCO 100 atthe node 101 will comprise a supplied input voltage 412 from the filter403. However, during sensing and programming operations (e.g., when thePLL 400 is powered on for the first time or when the VCO 100 otherwiserequires reprogramming), the signal 407 will be set (e.g., by controller170) at logic high so that the switch 409 is turned off and the switch410 is turned on. Thus, during sensing and programming operations, thefirst voltage 121 to the VCO 100 at the node 101 will be a predeterminedtuning input voltage supplied (not by the filter 403) but by a supplyvoltage 411 (Vset) having a fixed, pre-defined value. This fixed voltagevalue should optimally be set at the center of the VCO 100 input tuningrange.

Referring to FIG. 5, also disclosed herein are embodiments of anassociated method for operating a voltage controlled oscillator (VCO).The method embodiments comprise providing a VCO, such as the VCO 100described in detail above and illustrated in FIG. 1, for outputting aperiodic signal that has a frequency 123 as a function (e.g., anincrease function) of a first voltage 121 (i.e., either a supplied inputvoltage during an operational mode or a tuning input voltage during asensing mode) and, as necessary, a second voltage (i.e., a compensationvoltage) (505). Specifically, the provided VCO 100 can comprise aninductor-capacitor (LC) tank circuit 110 adapted to receive a firstvoltage 121 for controlling capacitance in the LC tank circuit 110 andat least one varactor 113 connected in parallel with theinductor-capacitor (LC) tank circuit 110 and adapted to receive a secondvoltage 122 for controlling capacitance in the varactor(s) 113. Theparallel connected LC tank circuit 110 and varactor(s) 113 can beconfigured such that the frequency 123 of the periodic signal at anoutput node 102 is a function of both the first voltage 121 and thesecond voltage 122. For example, increasing or decreasing either of thevoltages 121 or 122 will result in a corresponding increase or decrease,respectively, in the frequency 123 of the periodic signal at the outputnode 102.

Next, the provided VCO is powered up for the first time and a controlloop is established within the VCO 100 (510). In order to establish thecontrol loop at process 510, the VCO 100 is operated in two differentsequential modes: a sensing mode 515 and a programming mode 525. Thedifferent modes 515 and 525 can, for example, be controlledautomatically by a controller 160. In the sensing mode 515, adetermination is made as to whether the frequency 123 of the periodicsignal at the VCO output node 102 in response to a set first voltage 121(i.e., a predetermined tuning input voltage) is within a predeterminedfrequency range (516). Then, in the programming mode 525, if thefrequency is outside the predetermined frequency range, the resistancein a variable resistance e-fuse 170 that is electrically connected tothe varactor(s) 113 is selectively programmed to bring the frequency 123back into the predetermined frequency range by determining a requiredsecond voltage (i.e., a required compensation voltage and applying thatcompensation voltage to the varactor(s) 113(526). These different modesmay further be repeated, as necessary, until the frequency 123 is withinthe predetermined frequency range (530).

Specifically, in the sensing mode 515, the process 516 of determiningwhether or not the frequency 123 of the periodic signal at the VCOoutput node 102 in response to a set input voltage 121 (i.e., a tuninginput voltage) is within the predetermined frequency range can beaccomplished by determining a period of this periodic signal (517). Thisprocess 517 can be accomplished, for example, using a period detector140 connected to the amplifier 130. The detected period can be convertedinto an output voltage 124 (e.g., also by the period detector) (518).Through prior simulation and testing, it can be determined that anoutput voltage 124 that is above an upper limit of a predeterminedvoltage range indicates that the period is too long. This in turn willindicate that the frequency 123 of the periodic signal at the outputnode 102 is too low. Similarly, an output voltage 124 that is below alower limit of the predetermined voltage range indicates that the periodis too short. This in turn indicates that the frequency 123 of theperiodic signal at the output node 102 is too high. Thus, once theoutput voltage 124 is determined, a determination can also be made as towhether or not the output voltage 124 is within a predetermined voltagerange (519). This process 519 can be accomplished, for example using aplurality of voltage comparators 151-152 to compare the output voltage124 to the upper and lower limits of the predetermined voltage range.

Next, during the programming mode 525, the frequency 123 of the periodicsignal at the VCO output node 102 is adjusted, based on thedeterminations made at process 519 (526). Specifically, increasing ordecreasing the frequency 123 of the periodic signal at the VCO outputnode 102 can be accomplished by decreasing or increasing, respectively,the capacitance of the varactor(s) 113. Increasing or decreasing thecapacitance of the varactor(s) 113 can in turn be accomplished bydecreasing or increasing, respectively, a compensation voltage 122(i.e., a second voltage) applied to the varactors(s) 113. Finally,increasing or decreasing the compensation voltage 122 applied to thevaractor(s) 113 can in turn be accomplished by increasing or decreasing,respectively, the resistance of the variable resistance e-fuse 170.Thus, during programming 525, the resistance in the variable resistancee-fuse is selectively programmed so as to selectively adjust thecompensation voltage 122 at the varactor(s) 113, so as to selectivelyadjust capacitance of the varactor(s) 113, and further so as to bringthe frequency 123 of the periodic signal at the VCO output node 102 towithin the predetermined frequency range.

For example, at process 519 the output voltage 124 of the perioddetector 140 can be compared (e.g., using a first voltage comparator151) to the upper limit 125 of the predetermined voltage range todetermine if the frequency 123 of the periodic signal needs to beincreased. Then, the resistance in the variable resistance e-fuse 170can be selectively increased at process 526 so as to selectivelyincrease the compensation voltage 122 applied to the varactor(s) 113 inorder to selectively decrease the capacitance of the varactor(s) 113and, thereby to increase the frequency 123 of the periodic signal at theVCO output node 102, when the output voltage is higher than thepredetermined voltage range (527). Additionally, at process 519 theoutput voltage 124 can be compared (e.g., using a second voltagecomparator 152) to the lower limit 126 of the predetermined voltagerange to determine if the frequency 123 of the periodic signal needs tobe decreased. Then, the resistance in the variable resistance e-fuse 170can be selectively decreased at process 526 so as to selectivelydecrease the compensation voltage 122 at the varactor(s) 133 in order toselectively increase the capacitance of the varactor(s), and thereby todecrease the frequency 123 of the periodic signal at the VCO output node102, when the output voltage is lower than the predetermined voltagerange (528).

As mentioned above, the sensing and programming modes 515 and 525 can berepeated until it is determined that the output voltage 124 is withinthe predetermined voltage range and, thus, that the frequency 123 of theperiodic signal is within the predetermined frequency range (530).

The embodiments of the method, as described above, reference only asingle variable resistance e-fuse. Alternatively, the provided VCO 100can comprise a plurality of such variable resistance e-fuses 170 a-c(e.g., as illustrated in FIG. 3). Specifically, multiple variableresistance e-fuses 170 a-c can be connected in series. In this case, allof the resistors in any given variable resistance e-fuse 170 a-c will beequal in size. However, the resistors (e.g., 177 a, 177 b, 177 c) onadjacent variable resistance e-fuses 170 a-c will be progressivelysmaller in size (e.g., R for 177 a, R/10 for 177 b, R/100 for 177 c,etc.). With such a structure, the method embodiments can comprise finetuning the frequency 123 of the periodic signal at the output node 102.That is, each subsequent e-fuse (e.g., 170 a then 170 b then 170 c) canbe programmed in order to make smaller incremental changes in overallresistance and, thereby to make smaller incremental changes to thecompensation voltage 122 applied to the varactor(s) 113 in order toimprove compensation resolution.

In addition to the sensing and programming modes 515 and 525, describedabove, the VCO 100 of the present invention can also be operated in astandard operating mode, wherein a periodic signal is generated at theVCO output node 102 in response to a first voltage 121 supplied from anoutside device (525). For example, the VCO 100 can be incorporated intoa phase locked loop (PLL) circuit 400, as illustrated in FIG. 4, and thefirst voltage 121 to the VCO 100 can be provided by a filter 403 (e.g.,see item Vfilter 412).

The different modes can be controlled automatically using a controllerand a series of switches. Specifically, during the sensing mode 515, afirst current from a first current source 181 is forced (e.g., by meansof switches 191 and 192) to flow through the variable resistance e-fuse170 to the ground 183 in order to generate the compensation voltage 122at the varactor(s) 113. Thus, a determination can be made as to whetheror not frequency adjustment is required. In the standard operationalmode 540, the first current 181 from the first current source 181 issimilarly forced (e.g., by means of switches 191 and 192) to flowthrough the variable resistance e-fuse to the ground 183 in order togenerate the previously set compensation voltage 122 at the varactor(s)113. Thus, when the VCO 100 is powered on and in the standard operatingmode, the compensation voltage 122 will be continuously applied to thevaractor(s) 113 so that the VCO 100 operates within the predeterminedfrequency range. Contrarily, in the programming mode 525, a secondcurrent from a second current source 182 different from the firstcurrent source 181 is forced (e.g., by means of switches 193-196) toflow through the variable resistance e-fuse 170 in one direction oranother to program the resistance therein.

In addition to programming the resistance of the variable resistancee-fuse 170 at start-up, the method embodiment can also compriseoptionally readjusting the center frequency of the VCO 100 by performingthe sensing and programming modes 515 and 525 and resetting thecompensation voltage 122 (545). This reprogramming process 545 can beperformed at some point after the initial start-up, when alterativeprogramming is required or desired.

Also disclosed are embodiments of a design structure for the abovedescribed voltage controlled oscillator. Specifically, FIG. 6 shows ablock diagram of an exemplary design flow 600 used for example, insemiconductor design, manufacturing, and/or test. Design flow 600 mayvary depending on the type of IC being designed. For example, a designflow 600 for building an application specific IC (ASIC) may differ froma design flow 600 for designing a standard component. Design structure620 is preferably an input to a design process 610 and may come from anIP provider, a core developer, or other design company or may begenerated by the operator of the design flow, or from other sources.Design structure 620 comprises an embodiment of the invention as shownin FIGS. 1-3 in the form of schematics or HDL, a hardware-descriptionlanguage (e.g., Verilog, VHDL, C, etc.). Design structure 620 may becontained on one or more machine readable medium. For example, designstructure 620 may be a text file or a graphical representation of anembodiment of the invention as shown in FIGS. 1-3. Design process 610preferably synthesizes (or translates) an embodiment of the invention asshown in FIGS. 1-3 into a netlist 680, where netlist 680 is, forexample, a list of wires, transistors, logic gates, control circuits,I/O, models, etc. that describes the connections to other elements andcircuits in an integrated circuit design and recorded on at least one ofmachine readable medium. This may be an iterative process in whichnetlist 680 is resynthesized one or more times depending on designspecifications and parameters for the circuit.

Design process 610 may include using a variety of inputs; for example,inputs from library elements 630 which may house a set of commonly usedelements, circuits, and devices, including models, layouts, and symbolicrepresentations, for a given manufacturing technology (e.g., differenttechnology nodes, 32 nm, 45 nm, 90 nm, etc.), design specifications 640,characterization data 650, verification data 660, design rules 670, andtest data files 685 (which may include test patterns and other testinginformation). Design process 610 may further include, for example,standard circuit design processes such as timing analysis, verification,design rule checking, place and route operations, etc. One of ordinaryskill in the art of integrated circuit design can appreciate the extentof possible electronic design automation tools and applications used indesign process 610 without deviating from the scope and spirit of theinvention. The design structure of the invention is not limited to anyspecific design flow.

Design process 610 preferably translates an embodiment of the inventionas shown in FIGS. 1-3, along with any integrated circuit design or data(if applicable), into a second design structure 690. Design structure690 resides on a storage medium in a data format used for the exchangeof layout data of integrated circuits and/or symbolic data format (e.g.information stored in a GDSII (GDS2), GL1, OASIS, map files, or anyother suitable format for storing such design structures). Designstructure 690 may comprise information such as, for example, symbolicdata, map files, test data files, design content files, manufacturingdata, layout parameters, wires, levels of metal, vias, shapes, data forrouting through the manufacturing line, and any other data required by asemiconductor manufacturer to produce an embodiment of the invention asshown in FIGS. 1-3. Design structure 690 may then proceed to a stage 695where, for example, design structure 690: proceeds to tape-out, isreleased to manufacturing, is released to a mask house, is sent toanother design house, is sent back to the customer, etc.

Therefore, disclosed above are embodiments of a voltage controlledoscillator (VCO) capable of non-volatile self-correction to compensatefor process variations and, thereby to ensure that the center frequencyof the VCO is maintained within a predetermined frequency range.Embodiments of this VCO incorporate a pair of varactors connected inparallel to an inductor-capacitor (LC) tank circuit for outputting aperiodic signal having a frequency that varies as a function of an inputvoltage (e.g., increases with an increasing input voltage, decreaseswith a decreasing input voltage). The embodiments further incorporate acontrol loop. This control loop uses programmable variable resistancee-fuse(s) to set a compensation voltage to be applied to the pair ofvaractors. By adjusting the compensation voltage, the capacitance of thepair of varactors can be adjusted in order to selectively increase ordecrease the frequency of the periodic signal in response to an inputvoltage and, thereby bring the frequency of that periodic signal intothe predetermined frequency range. Also disclosed are embodiments of anassociated design structure for such a VCO and an associated method foroperating such a VCO.

The above-described embodiments of the present invention providemultiple benefits over prior art VCO process variation compensationtechniques. Specifically, they allow for VCO process variationcompensation with minimal area costs, without reducing the Q value ofVCO and with high resolution (e.g., when multiple e-fuses connected inseries are programmed to establish the compensation voltage). Theembodiments further allow for non-volatile compensation. That is, theprogrammed resistance in the e-fuse(s) and, thereby the establishedcompensation voltage is maintain even when power to the VCO is off.Thus, compensation programming is only required at initial start-up,with reprogramming being optional.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without departing from the generic concept,and, therefore, such adaptations and modifications should and areintended to be comprehended within the meaning and range of equivalentsof the disclosed embodiments. It is to be understood that thephraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the invention hasbeen described in terms of embodiments, those skilled in the art willrecognize that these embodiments can be practiced with modificationwithin the spirit and scope of the appended claims.

1. A voltage controlled oscillator comprising: an inductor-capacitor(LC) tank adapted to receive a first voltage; at least one varactorconnected in parallel with said LC tank and adapted to receive a secondvoltage; an output node connected to said LC tank and said at least onevaractor for outputting a periodic signal having a frequency that is afunction of said first voltage and said second voltage; a variableresistance e-fuse adapted to apply said second voltage to said at leastone varactor; and a controller adapted to program resistance in saidvariable resistance e-fuse, when said frequency is outside apredetermined frequency range, so as to selectively adjust said secondvoltage, so as to adjust capacitance of said at least one varactor, andfurther so as to bring said frequency of said periodic signal to withinsaid predetermined frequency range.
 2. The voltage controlled oscillatoraccording to claim 1, further comprising: a period detector adapted todetermine a period of said periodic signal and to convert said periodinto an output voltage; and a plurality of voltage comparators adaptedto determine if said output voltage is within a predetermined voltagerange, wherein said controller is in communication with said pluralityof comparators and is adapted to program said resistance to selectivelyadjust said second voltage, when said output voltage is outside saidpredetermined voltage range, so as to bring said frequency to withinsaid predetermined frequency range.
 3. The voltage controlled oscillatoraccording to claim 2, wherein said controller is adapted to selectivelyincrease said resistance so as to increase said second voltage in orderto decrease said capacitance and, thereby increase said frequency, whensaid output voltage is higher than said predetermined voltage range, andwherein said controller is further adapted to selectively decrease saidresistance so as to decrease said second voltage in order to increasesaid capacitance and, thereby decrease said frequency, when said outputvoltage is lower than said predetermined voltage range.
 4. The voltagecontrolled oscillator according to claim 1, wherein said variableresistance e-fuse comprises: a conductor; a plurality of seriesconnected resistors; a plurality of contacts on said conductor connectedto said plurality of said series connected resistors; a first sensingnode and a second sensing node on opposite ends of said the seriesconnected resistors, wherein said first said sensing node iselectrically connected to said at least one varactor for applying saidsecond voltage to said at least one varactor and said second sensingnode is electrically connected to ground; and a first programming nodeand a second programming node on opposite ends of said conductor, andwherein said controller is adapted to control current flow through saidconductor between said first programming node and said secondprogramming node such that said contacts one of become opens in sequenceto increase said resistance and revert back to shorts in sequence todecrease said resistance.
 5. The voltage controlled oscillator accordingto claim 4, wherein said resistors are all equal in size.
 6. The voltagecontrolled oscillator according claim 4, further comprising a pluralityof said variable resistance e-fuses connected in series, wherein all ofsaid resistors in any given variable resistance e-fuse are equal in sizeand wherein said resistors on adjacent variable resistance e-fuses areprogressively smaller in size so as to allow for fine tuning of saidfrequency.
 7. The voltage controlled oscillator according to claim 1,further comprising a first current source for generating said secondvoltage and a second current source different from said first currentsource for programming said resistance.
 8. The voltage controlledoscillator according to claim 1, further comprising an amplifierelectrically connected between said varactor and said control loop so asto magnify said periodic signal.
 9. The voltage controlled oscillatoraccording to claim 1, wherein said resistance is non-volatile andreprogrammable.
 10. A design structure for a voltage controlledoscillator, said design structure embodied in a machine readable mediumand said voltage controlled oscillator comprising: an inductor-capacitor(LC) tank adapted to receive a first voltage; at least one varactorconnected in parallel with said LC tank and adapted to receive a secondvoltage; an output node connected to said LC tank and said at least onevaractor for outputting a periodic signal having a frequency that is afunction of said first voltage and said second voltage; a variableresistance e-fuse adapted to apply said second voltage to said at leastone varactor; and a controller adapted to program resistance in saidvariable resistance e-fuse, when said frequency is outside apredetermined frequency range, so as to selectively adjust said secondvoltage, so as to adjust capacitance of said at least one varactor, andfurther so as to bring said frequency of said periodic signal to withinsaid predetermined frequency range.
 11. The design structure accordingto claim 10, wherein said design structure comprises a netlist.
 12. Thedesign structure according to claim 10, wherein said design structureresides on storage medium as a data format used for the exchange oflayout data of integrated circuits.
 13. The design structure accordingto claim 10, wherein said voltage controlled oscillator furthercomprises: a period detector adapted to determine a period of saidperiodic signal and to convert said period into an output voltage; and aplurality of voltage comparators adapted to determine if said outputvoltage is within a predetermined voltage range, and wherein saidcontroller is in communication with said plurality of comparators and isadapted to program said resistance to selectively adjust said secondvoltage, when said output voltage is outside said predetermined voltagerange, so as to bring said frequency to within said predeterminedfrequency range.
 14. A voltage controlled oscillator comprising: aninductor-capacitor (LC) tank adapted to receive a first voltage; atleast one varactor connected in parallel with said LC tank and adaptedto receive a second voltage; an output node connected to said LC tankand said at least one varactor for outputting a periodic signal having afrequency that is a function of said first voltage and said secondvoltage; a variable resistance e-fuse adapted to apply said secondvoltage to said at least one varactor; and a controller adapted toprogram resistance in said variable resistance e-fuse, when saidfrequency is outside a predetermined frequency range, so as toselectively adjust said second voltage, so as to adjust capacitance ofsaid at least one varactor, and further so as to bring said frequency ofsaid periodic signal to within said predetermined frequency range,further comprising: a period detector adapted to determine a period ofsaid periodic signal and to convert said period into an output voltage;and a plurality of voltage comparators adapted to determine if saidoutput voltage is within a predetermined voltage range, wherein saidcontroller is in communication with said plurality of comparators and isadapted to program said resistance to selectively adjust said secondvoltage, when said output voltage is outside said predetermined voltagerange, so as to bring said frequency to within said predeterminedfrequency range.
 15. The voltage controlled oscillator according toclaim 14, wherein said controller is adapted to selectively increasesaid resistance so as to increase said second voltage in order todecrease said capacitance and, thereby increase said frequency, whensaid output voltage is higher than said predetermined voltage range, andwherein said controller is further adapted to selectively decrease saidresistance so as to decrease said second voltage in order to increasesaid capacitance and, thereby decrease said frequency, when said outputvoltage is lower than said predetermined voltage range.
 16. The voltagecontrolled oscillator according to claim 14, wherein said variableresistance e-fuse comprises: a conductor; a plurality of seriesconnected resistors; a plurality of contacts on said conductor connectedto said plurality of said series connected resistors; a first sensingnode and a second sensing node on opposite ends of said the seriesconnected resistors, wherein said first said sensing node iselectrically connected to said at least one varactor for applying saidsecond voltage to said at least one varactor and said second sensingnode is electrically connected to ground; and a first programming nodeand a second programming node on opposite ends of said conductor, andwherein said controller is adapted to control current flow through saidconductor between said first programming node and said secondprogramming node such that said contacts one of become opens in sequenceto increase said resistance and revert back to shorts in sequence todecrease said resistance.
 17. The voltage controlled oscillatoraccording to claim 16, wherein said resistors are all equal in size. 18.The voltage controlled oscillator according claim 16, further comprisinga plurality of said variable resistance e-fuses connected in series,wherein all of said resistors in any given variable resistance e-fuseare equal in size and wherein said resistors on adjacent variableresistance e-fuses are progressively smaller in size so as to allow forfine tuning of said frequency.
 19. The voltage controlled oscillatoraccording to claim 14, further comprising a first current source forgenerating said second voltage and a second current source differentfrom said first current source for programming said resistance.
 20. Thevoltage controlled oscillator according to claim 14, further comprisingan amplifier electrically connected between said varactor and saidcontrol loop so as to magnify said periodic signal.